A 2-dimensional Fourier transform method for the quantitative measurement of Lamb modes

The key problem associated with the quantitative measurement of the characteristics of propagating Lamb waves is that more than one wave mode can exist at any given frequency. Therefore, a simple Fourier transformation from the time to the frequency domain cannot distinguish between the different modes. A 2-D Fourier transform technique involving both spatial and time transformations from which the required information can be obtained is presented. The results obtained from both numerical and experimental investigations of Lamb waves propagating in steel plates are presented using an isometric projection, which gives a 3-D view of the wave-number dispersion curves. The results show the effectiveness of using the 2-D Fourier transform method to identify and measure the amplitudes of individual Lamb modes